Rotary bowl mill



March 29, A193s.

J. CRITES m' f "f7 .fae

2 Sheets-Sheet 1 r ImenSn [71 es March 29, 1938.

J. CRITES ROTARY owrJ MILL Filed June 29, 1936 2 Sheets-Sheet 2 1 v 407 Il f 1./ W V Patented Mar. 29, 1938 PATENT OFFICE ROTARY BOWL MILL Joe Crites, Evanston, lll., assignor, by mesne assignments, to Combustion Engineering Company, Inc., a corporation of Delaware Application June 29, 1936, Serial No. 87,928

6 Claims.

This invention relates to certain new and useful improvements in a rotary bowl mill adapted to grind and pulverize solid materials, such as coal, rock, etc.

Brieily described, the mill is of the type including an upwardly opening bowl or container which is rotatable about a central vertical axis within a substantially closed housing or casing. One or more grinding rollers, each freelyv rotatable about its own axis, are suspended within the bowl so as to be forced under pressure toward the upwardly and outwardly projecting inner side wall of the bowl, or the material carried thereby, the rollers being rotated by contact with this material. The side walls of the bowl are spaced from the side walls of the container so as to provide an annular air passage around the bowl, air being admitted to the lower portion of the casing and drawn or forced under pressure through the annular passage with a whirling motion, and thence over the bowl and through outlets in the upper wall of the casing to a separator. Sumciently pulverizedA material is carried in suspension in the air stream from the casing into and through the separator. The material to be pulverized is introduced from above into the central portion of the bowl, and insuiilciently pulverized material is also returned from the separator into the central portion of the bowl Stationary de-l flectors are positioned in the casing at the outer side of and above the annular air passage to return insuiiiciently pulverized material thrown from the bowl back into the bowl for further treatment. "Ihe heaviest waste materials fall through the annular passage into the lower portion of the casing or housing, and Scrapers carried by the rotating bowls` direct this material toward a discharge opening in the bottom of the casing. A mill of the general type described hereinabove is disclosed and claimed inapplicants former application Serial No. 25,789, led June 10, 1935.

In -a mill of this type, it has been found that some of the heavier material particles thrown from the rotating bowl and not suihciently pulverized do not reach the stationary deiiectors, or are not returned to the bowl thereby, and these heavier material particles find their way downwardly into the whirling air stream in the annular passage between the casing and the upwardly and outwardly extending side wall of the rotating bowl. The purpose of the present improvements is to provide means for returning this ma terial to the bowl for further grinding treatment. More specically, spiral ribs or vanes are provided on the wall of the casing at the outer side of the air passagefthese ribs being inclined upwardly .in the direction of rotation of the air stream. The whirling materials are held closely against the casing wall and are guided by these 5 ribs upwardly toward the deflectors by' which they are thrown back into the bowl.

The principal object of this invention is to provide an improved bowl mill of the type brieiiy described hereinabove and disclosed more in de- 10 tail in the specifications which follow.

Another object is tn provi'de improved means for returning into the bowl for further treatment such grindable materials as iind their way into the annular air passage surrounding the bowl.

Another object is to provide improvedvspiral directing ribs in the mill casing for directing ma.- terials upwardly through the air passage.

Another object is to provide spiral deilecting ribs in combination with stationary deflectors for returning material into the grinding bowl.

Other objects and advantages of this invention will be more apparent from the following detailed .description of one approved form of mill constructed and operating according to the principles of this invention.

In the accompanying drawings:

Fig. 1 is a central vertical section the improved mill assembly.

Fig. 2 is a partial plan view and partial hori- 30 zontal section. The upper left-hand portion of this figure is taken substantially on the line 2--2 of Fig. 1, whereas the right-hand portion is taken substantially .on the line 22' of Fig. 1.

Fig. 3 is a perspective view oi.' the inner por- 35 tion of one side of the mill casing, showing the stationary spiral ribs and deflecting vanes.

This assembly comprises the casing or housing A, the rotatable bowl or container B which is driven and supported by the mechanism indicated generally at C, the grinding rollers D, and the mechanisms indicated generally at E for` supporting and exerting adjusted pressure on the rollers. The means shown at F feeds material to be ground into the mill, and the conduit system indicated generally at G delivers air under pressure into the lower portion oi' the mill housing. At H is indicated generally the mechanisms ,for discharging waste materials from the mill.

while at K is shown the separator through which the suiciently pulverized material is carried out in suspension and from which insuiiiciently pulverized material is delivered back into the bowl B.

At L is indicated generally the devices which more particularly form the subject matter of this through invention, for returning insufficiently pulverized material thrown from the bowl back into the bowl for further grinding treatment.

'I'he enclosing casing or housing A comprises the base plate I which rests upon the concrete pedestals or foundation 2, the annular side wall 3, and the closure or cover plate 4. The base plate I comprises a central bearing portion 5 in which the hub 6 of bowl B is journaled. The annular side wall 3 comprises a lower substantially cylindrical portion 1, a central upwardly diverging portion 8, and an upper, somewhat larger cylindrical portion 9 to the upper edge of which the cover plate 4 is secured. This side wall may be provided with a suitable liner indicated generally at I0. The cover plate 4 is provided witha plurality of openings I I each closed by an individual cover plate I2. Each opening II permits the insertion or removal of one of the roller assemblies D, and the roller supporting and adjusting mechanism E is carried by the cover plate I2. The main cover plate 4 is also provided with a plurality of outlet openings I3 which communicate with passages leading up into the separator K. A central opening I4 in cover plate 4 communicates with the lower discharge end of the separator K, as will be hereinafter described. Except for the openings referred to above, the top of the casing may be considered as entirely closed.

'I'he bowl or container B comprises a central shallow table portion I5 formed by a. disk-like bottom wall which slopes upwardly and outwardly at a small angle to the horizontal from the central axis of rotation, and an annular grinding wall formed by an upwardly projecting outer ange portion I6 which ares outwardly at a small angle to the vertical. Preferably the-inclination of the outer bowl wall I6 is substantially the same as that of the adjacent casing wall 8 so as to leave an annular air passage I1 therebetween, as hereinafter described. Preferably a separate grinding track or ring I8 is mounted on the inner surface of the inclined side Wall I6 of the bowl.

The driving assembly C comprises a central vertical drive shaft I9 which is keyed Within the hub 6 of the bowl B. The upper and lower members 28 and 2i of a gear casing are secured together and to the base plate I so as to enclose and lubricatethe gears for rotating shaft I9. A worm wheel 22 keyed on shaft I9 meshes with and is driven by a worm 23 suitably journaled in the gear casing and connected with a driving motor or other suitable driving means not here shown. f

There may be one or more of the grinding rollers D, depending on the size of the mill, there being three of these rollers in the example here shown. These rollers will be equally spaced about the central axis so as to distribute the thrust on the grinding bowl B. Each roller comprises a removable and renewable grinding tread 24 carried by the sleeve assembly 25 which is freely rotatable on the non-rotary supporting shaft 26. This type of grinding roller is well known in the art and need not be here described in detail. The roller 24 is rotatable by contact with the grinding ring I8, or more properly by contact with the material to be ground which is interposed between the tread 24 of the roller and the grinding ring I8 as will be hereinafter apparent. Preferably the vertical axis of the bowl, the central axis of rotation of each grinding roller D, and the apexes of the conical grinding surfaces of the rollers D and the grinding ring I8, all

meet in a common point positioned below the bowl so that there will be a true rolling engagement between the surfaces of the rollers and grinding ring.

The shaft 26 projects up through an opening 21 in cover plate I2 and the tapered upper end portion 28 of shaft 26 is secured in the hub 29 of the lever mechanism indicated generally at E by means of which the roller assembly is supported and adjusted. This lever comprises a split hub 30 which is locked on the central portion of a short horizontal shaft 3I which is journaled at its ends in brackets 32 projecting upwardly from the cover plate I2. A compression spring 33 is confined between the outwardly projecting end portion 34 of the lever E, and a plate 35 adjustably supported by bolts 35' from the cover plate I 2. This spring tends to swing the lever mechanism E in a clockwise direction, as seen in Fig. 1, so as to force the roller D toward the grinding ring I8. Preferably an adjustable limiting plate 36 carried by the upper ends of the bolts 35 serves to limit the movement of the roller in this direction so that a slight clearance will remain at all times between the surface of the grinding roller and vthe grinding ring I8. It will be apparent that spring 33 tends to swing the lever E about its pivot so as to move the roller D toward the grinding ring I 8. As material to be ground finds its way between roller D and grinding ring I 8, the spring 33 will yield to permit the roller to swing inwardly, but will exert a predetermined outward pressure on this material, the pressure being determined by proper adjustment of the spring mechanism. In case there is no material on the grinding ring I8, the small clearance provided will prevent hammering of the rollers cn the grinding ring and thus reduce noise and wear on the grinding surfaces.

It will be understood that the above description isof one of the roller units D and E, each of these units consisting of an assembly such as just described hereinabove. dividual cover plate I2, each of these grinding units can be removed and the roller lifted out of the housing through opening il.

'I'he material to be ground and pulverized is fed into the housing by the feed mechanism F, which in the example here shown comprises a hopper 3'I, a rotary feeder 38, a horizontal screw conveyor 39, and a chute 40 which extends down into the bowl B through one of the openings I3 in the top wall 4 of the housing.

Air from any suitable source is delivered through pipe or conduit 4I into the pipe extension 42 of casing wall 3. This air passage extends tangentially into the lower portion of the mill housing through inlet opening 43 so as to create a whirling movement of the air within the housing. This air is delivered into the housing under pressure, but this pressure may be created by a suction at the outlet of separator K. 'I'his air stream, the whirling movement of which will be increased by the rotation of bowl B which rotates in a clockwise direction as viewed from above, passes upwardly through the annular channel I1 between the rotating bowl and the side wall 8 of the casing, thence inwardly over the bowl and out through the openings I3 in the cover plate into the separator K.

The material in bowl B will move by centrifugal force toward the outer walls I6 of the bowl and will be ground and pulverized between the By removing the inl rollers Dand the grinding ring I8. Due to the small outward inclination of the outer walls I6 of the bowl, centrifugal force will hold a compact bed of the material against the grinding ring I8, through which bed of material -the rollers D grind, and this material will move slowly upwardly before being thrown or discharged from the upper edge of the bowl. A plurality of stationary deilectors 44 are positioned at spaced intervals circumferentially of the housing in the upper and outer portion thereof adjacent the side wall 9 and top wall 4. These deflectors are at the outer side of and above the annular air passage I1, and are in the form of substantially vertical vanesvwhich extend diagonallyinward from the outer wall 9 in the direction of rotation of the bowl. A movable annular deflector indicated generally at 45 is mounted on the upper edge portion of the side wall I6 of the bowl. This deflector may be provided with an inner surface sloping upwardly and outwardly toward the stationary deectors 44, or may be in the form of an annular angleplate such as here shown. Material from the bowl will till in this angle so as to provide an upwardly and outwardly sloping surface, and material which would otherwise be thrown substantially horizontally by centrifugal force will be directed upwardly and outwardly by this sloping surface toward the stationary deilector vanes 44. Due to the rather lrapid rotation of bowl B this discharged material will be thrown forwardly or tangentially substantially in the direction of rotation of the bowl, and at the same time will be directed upwardly so as to contact with the stationary deilectors 44. 'I'his material is also projected through the air stream which is moving spirally upward through the annular passage I1', this air stream assisting the centrifugal force `imparted by the bowl to carry the material forwardly andupwardly into forcible engagement with the stationary deilectors 44. The air stream is of sulcient volume and velocity to carry sumciently pulverized materialin suspension, and such material will be maintained in suspension by the air stream andeventually carried out through the upper outlet openings I3. Larger particles of material which have not been suiciently pulverized o r reduced in size and -which are too heavy to be carried out in suspension in the air stream will be thrown back through the air stream by the deflecting vanes 44 into the central portion of the bowl B and thus returned through the grinding cycle. The heavier and larger particles of waste material which cannot be ground in the mill and are to be rejected are thrown outwardly from the bowl in a more horizontal direction and fall back through passage I1 into the lower chamber 46 beneath the bowl.

The discharge mechanism H comprises a dischargel opening 41 extending down from chamber 46 through the base plate I and communieating with the discharge chute 48. A downwardly opening one-way valve 49 permits this waste material to flow out through chute 48 while minimizing the inflow of air through this chute. A plurality of Scrapers 50 are pivotally mounted at their inner ends on the lower portion of bowl B so as to swing outwardly by centrifugal force as the bowl is rotated. IIi'hese scrapers carry material deposited in chamber 46 around into position,` to be discharged through opening 41. Lightermaterial `stirred up by these scrapers will be carried up by the whirling air stream through passage I1 and thence returned into the mill.

The mill as hereinabove described is substantially of the general type disclosed and claimed in the copending application of Crites, Serial No. 25,789, hereinabove referred to. In the operation of this mill it has been found that some insuniciently pulverized material which is suitable for further grinding, and which it is not desired to discharge through chute 48 as waste material, finds its way into the air passage I1 between the rotating bowl B and the casing A. These material particles may be too heavy to reach the deflectors 44 and rebound into the mill, or may be thrown out in such a direction as to miss the deectors 44, or for some other reason these heavier material particles find their4 way into the air passage I1. These material particles will be caused to rotate or whirl in this passage I1 closely adjacent the casing wall 8, or the liner Ii! therein. According to the present improvements, the liner sections I within the portion 8 of the easing wall are formed with upwardly inclined ribs I, which may be in the form of portions of spirals extending in the general direction of the whirling air currents. These ribs `need only extend partially across the air passage, since all of the whirling materials will' follow quite closely against the inner surface of the liner plates I0'. The whirling materials will engage with the upper surface of the ribs 5I and be directed upwardly so as to eventually contact the stationary deflectors 44 and be thrown back into the bowl. As a result of this improvement there is less waste through the discharge chute 48 anda greater percentage of the material is eventually pulverized to the desired extent and carried out in' the air stream into separator K.

The separator K may take a variety of forms, lt being here shown as of the general type disclosed and claimed in the copending application of Crites, Serial No. 62,450, filed February 5, 1936. The passages 52 extend upwardly from the outlet opening I3 and then expand upwardly, outwardly and circumferentially to merge into the annular chamber 53 at the upper end of the separator. This annular chamber 53 communicates through a series of openings 54 in its inner wall with the central expansion chamber 55. The vanes or deectors 56 at the sides of openings 54 impart a whirling movement to the air entering expansion chamber 55. This air stream, carrying-the suiliciently pulverized material in suspension, will be drawn out through the central conduit 51 which projects down at its lower end into expansion chamber and which connects at its upper end with a suitable pipe or conduit 58 leading to a separator or other place of discharge Where the pulverized material is withdrawn from the air stream. lnsufliciently pulverized material drops out of the air stream in the expansion chamber 55 and is directed by the conical lower portion 59 downwardly `and through central chute I4 into the grinding bowl B. l Since there is a tendency for air to be drawn upwardly from the mill housing through opening I4 and directly out through the upper central outlet 51, means is preferably provided to prevent insufficiently pulverized material from being carried out in such an air stream. In some installations, some type of one-way valve is provided in the discharge outlet I4. As here shown a hollow conical deector 60 with its larger end at the bottom is supported within the lower central portion of the separator. A plurality of spiral vanes 6I are mounted on the inner walls of cone 59 below the deector 60. The deiiector 60 serves a twofold function. In the iirst place its tapered upper surface tends to puncture the vortex formed by the whirling air stream and thus prevents materials being sucked up through the center of the vortex and out through the upper outlet opening. In the second place, air tending to flow up through the center of the bottom discharge opening I4 will be caught by the lower end portion of this cone and forced to flow outwardly toward the side walls of cone 59. This air will be caused to join in the whirling motion of the larger air stream within this cone 59, and any materials that have been picked up by this upwardly flowing air current will be thrown outwardly against the walls of the cone and caught beneath the vanes 6I and thus carried downwardly toward the discharge outlet I4. As a result substantially none of the heavier material or tailings can be carried upwardly through th'e central portion of the separator or classifier even though this bottom discharge outlet I4 is open at Aall times.

I claim:

1. A mill comprising a closed casing, a bowl mounted within the casing for rotation about a central vertical axis, means for rotating the bowl, means for introducing into the bowl material to be ground, means within the bowl for grinding the material, there being an annular air passage between the outwardly and upwardly extending outer wall of the bowl and the enclosing wall of the casing, means for forcing air under pressure upwardly through the passage with a whirling motion in the direction of rotation of, the bowl, non-rotary defiecting vanes positioned in the casing at the outer side of and above the passage for directing material thrown from the bowl back through the air stream into the bowl, and ribs carried by the casing wall at the outer side of the air passage and inclined upwardly in the direction of movement of the whirling air stream for directing material in the passage toward the defiecting vanes.

2. A mill comprising a closed casing, a bowl mounted within the casing for rotation about a central vertical axis, means for rotating the bowl, means for introducing -into the bowl material to be ground, means within the bowl for grinding the material, there being an annular air passage between the outwardly and upwardly extending outer wall of the bowl and the enclosing wall of the casing, means for forcing air under pressure upwardly through the passage with a whirling motion in the direction of rotation of the bowl, non-rotary deilecting vanes positioned in the casing at the outer side of and above the passage for directing materialtthrown from the bowl back through Ythe air stream into the bowl, and spiral ribs carried by the casing wall at the outer side of the air passage and inclined upwardly in the direction of movement of the whirling air stream for directing material in the passage toward the defiecting vanes.

3. A mill comprising a closed casing, a bowl mounted within the casing for rotation about a central vertical axis, means for rotating the bowl, means for introducing material to bev ground into the central portion of the bowl, freely rotatable grinding 'rollers suspended within the bowl in position to be rotated by contact with the material carried on the inner surface of the outer wall of the bowl, there being an annular passage between the outwardly and upwardly extending outer wall of the bowl and the enclosing wall of the casing, an inlet opening in the lower portion of the casing through which air is delivered under pressure, an outlet opening for the air stream in the upper portion of the casing, nonrotary deiiecting vanes positioned inv the casing upwardly and outwardly from the periphery of .the bowl at the outer side of the air passage for deecting material thrown thereagainst from the bowl back through the air stream into the bowl, and ribs carried by the casing at the outer side of the air passage and inclined upwardly in the direction of rotation of the bowl for directing material in said passage toward the deflecting vanes.

4. A mill comprising a closed casing, a bowl mounted within the casing for rotation about a central vertical axis, means for rotating the bowl, means for introducing material to be ground into the central portion of the bowl, freely rotatable grinding rollers suspended within the bowl in position to be rotated by contact with the material carried on the inner surface of the outer wall of the bowl, there being an annular passage between the outwardly and upwardly extending outer wall of the bowl and the enclosing wall of the casing, an inlet opening in the lower portion of the casing through which air is delivered under pressure, an outlet opening for the air stream in the upper portion of the casing, non-rotary deecting vanes positioned in the casing upwardlyand outwardly from the periphery of the bowl at the outer side of the air passage for deflecting material thrown vthereagainst from the bowl back through the air stream into the bowl, and spiral ribs carried by the casing at the outer side of the air passage and inclined upwardly in the direction of rotation of the bowl for directing material in said passage toward the deecting vanes.

5. Amill comprising a closed casing, a grinding member having an upper grinding surface, said member being mounted within the casing for rotation about a central vertical axis, means for rotating the member, means for introducing material to be ground onto the upper grinding surface of the member, means cooperating with this grinding surface for grinding the material, there being an annular air passage between the outer periphery of the member and the enclosing wall of the casing, means for forcing air under pressure upwardly through the passage with a whirling motion in the direction of rotation of the grinding member, non-rotary deflecting vanes positioned in the casing at the outer side of and above the air passage, means on the peripheral portion of the rotary grinding member for directing material thrown from the member toward the vanes, this material being thrown back from the vanes onto the member and ribs carried by the casing wall at the outer side of the air passage and inclined upwardly in the direction of movement of the whirling air stream for directing material at the outer side of the passage upwardly toward the vanes.

6. A mill comprising a closed casing, a grinding member having an upperl grinding surface, said member being mounted within the casing for rotation about a central vertical axis, means for rotating the member, means for introducing material to be ground onto the upper grinding surface of the member, freely rotatable grinding rollers suspended above the member in position to be rotated by contact with the material carried on thevgrix'd'ingff'surface,- there being an annular air passage between the outer periphery of the member and the enclosing wall oi the casing, an inlet opening in the .lower portion o! the casing through which air is delivered under pressure', an outlet opening for the air stream and suspended material leading from the upper portion of the casing, non-rotary deecting vanes positioned in the casing at the outer side of and m above the air passage-'manson the peripheral portion of the rotary grinding member forI directing material thrown from the member toward `the vanes, this material being thrown back from the vanes onto the member, and ribs Vcarried by the casing wall at the outer side of the air passage and inclinedgupwardly in the direction o i `movement o! the whirling air stream i'or directing material at the outer side of the passage up- .oE cRn'Es. 10

wardly toward the vanes. 

